(1) Field of the Invention
The present invention relates to an optical pickup device which records and reproduces information to and from an optical disk in an optical disk drive unit and, more particularly, to a technique to fix an optical part in an optical pickup device.
(2) Description of the Related Art
Optical pickup devices which are used to record and reproduce information to and from optical disks such as CDs, DVDs, Blu-ray discs making use of blue semiconductor lasers, and HD-DVDs have a structure in which: a beam from a light-emitting device such as a laser diode is led to an objective lens via various lenses, prisms, and mirrors; the beam is focused on an optical disk; and the light reflected from the optical disk is received, for conversion into a photoelectric signal, by a photodiode via various lenses and mirrors including the objective lens.
In such a structure, optical parts including various lenses are fixed, with submicron accuracy, at predetermined locations on an optical path in a pickup case. Generally, to fix an optical part in a pickup case included in an optical pickup device: the optical part is positioned using a jig; an ultraviolet-curing adhesive is applied to a predetermined area; and the adhesive is cured by ultraviolet ray irradiation. When, in such a structure, an optical part is fixed in position using an ultraviolet-curing adhesive, however, the optical part can be positionally shifted, not to be restored into position, to degrade the reliability of the optical pickup device. Such positional shifting of the optical part can be caused, for example, by changes in ambient conditions or variations in the area where the adhesive is applied or in the amount of adhesive application. Furthermore, to allow an adhesive to securely cure into a stable condition, it is necessary to secure adequate annealing time and ultraviolet ray irradiation time at a sacrifice of productivity.
To cope with the above problems, fixing an optical part to a pickup case by laser welding instead of using an adhesive has been proposed as a method which can improve the positional stability of the optical part and increase productivity while securing adequate joint strength between the optical part and the pickup case.
In Japanese Patent Laid-Open No. 2004-20867, it is proposed to reduce the cost of producing a film unit having plural components including lenses by laser welding a plastic spherical lens to a cover without using any adhesive or any special tool.
In Japanese Patent Laid-Open No. 2004-354438, a method of joining a resin optical part to a resin holder is proposed. In the method, a laser beam is applied to the resin holder in an environment where an inactive gas is spewed, and molten resin is allowed to deposit on the optical part, thereby realizing a joint to cause no aberration.
In Japanese Patent Laid-Open No. 2005-316044, a lens fixing method for a lens unit which includes a lens and a lens frame is proposed. In the method, a lens to be included in a lens unit is first fitted in the lens unit, and an outer peripheral portion of the lens is then laser welded. In this way, the lens can be quickly fixed in the lens unit with high accuracy.